The overall objective of the proposed research is to dissect the role of SV40 tumor or T antigen in the expression of SV40 transplantation rejection antigen (TrAg) at surface SV40 infected or transformed cells. We have demonstrated that the TrAg antigenic sites exist on T antigen, however, the distribution of these sites on T antigen remains unknown. We now propose to determine (1) the segments of SV40 early region which are involved in TrAg expression, (2) the localization of SV40 early gene products at the surface of SV40 infected and transformed cells, (3) whether T antigen at the cell surface directly acts as a target for cytotoxic lymphocytes, (4) domains of T antigen which possess TrAg activity, and (5) to compare TrAg specified by SV40 and the related human papovavirus BK in mouse cells transformed by these viruses. The approaches described above will allow us to seek evidence for the direct relationship between SV40 T antigen and TrAg recognized by the cytotoxic lymphocytes by using genetic, immunological and recombinant DNA approaches.